The number of political special advisers working in Downing Street and across Whitehall has risen back to the peak levels under Tony Blair, despite the coalition's pledge to dramatically cut back on the posts.

Francis Maude, the Cabinet Office minister, blamed "unusual forces of the coalition" for the rise in special advisers, which breaks the spirit of both the Conservative election manifesto and the coalition agreement.

The Tory manifesto pledged to cut "the scope of Whitehall", and the coalition agreement pledged to "put a limit on the number on [sic] special advisers". Numbers were cut to 66, a dozen fewer than in the last days of the Labour government in 2010.

Maude told MPs the number had now reached 85 – thought to be exactly the number employed by Labour in 2004. It was 81 at the last report in December.

"No one had at that stage [the coalition agreement] thought through the implications in a coalition," Maude told the public administration select committee.

On Tuesday the minister will unveil the government's civil service reform plan, which he has been working on with Sir Bob Kerslake, the head of the civil service. Maude will announce two key changes:

• All permanent secretaries in what are known as the main delivery departments, such as health and education, will be required to have had more than two years in a commercial or operational role. Maude, whose plans are based on a consultation process with staff across the country, is keen to provide opportunities to the 70% of civil servants outside Whitehall who do not fit into the Yes Minister policymaking mould.

• A more rigorous appraisal system, which will identify the top 25% and the bottom 10%. The high performers will be recognised while the poor performers will be "tackled".

Maude's admission on the rise of special advisers came as the public administration select committee took evidence on the second and final day of an inquiry into the role and accountability of special advisers, which are employed as temporary civil servants but allowed to give political advice.

The inquiry follow a series of scandals and concerns, including over Andy Coulson, the former News of the World editor who became David Cameron's media spokesman, and Adam Smith, who stepped down as Jeremy Hunt's special adviser after it was revealed he had exchanged 500 emails, text messages and phone conversations with News International while Hunt was considering whether the company should be allowed to take control of BSkyB. Last year the defence secretary Liam Fox resigned over the conduct of his unofficial adviser Adam Werritty.

Under questioning from MPs, Sue Gray, head of propriety and ethics at the Cabinet Office, revealed she had "not particularly" been consulted or asked to look into the concerns about Coulson or Smith, and said she did not see her role as a "compliance officer".

However, Gray defended the system: "Everybody had a copy of their code, everybody is meant to know what's in their code, and compliance with that code would rely on all the civil servants and special advisers to comply with it," she said.

Maude said that if the permanent secretary of a department had concerns about the behaviour of a special adviser they should first report that to the minister, and if they were not happy it had been dealt with they should go to the head of the civil service.